Agomelatine with chemical name N-[2-(7-methoxy-1-naphthyl)ethyl]acetamide and brand name Valdoxan has the following formula:

Agomelatine has dual effects by acting as an agonist of melatoninergic system receptors and as an antagonist of the 5HT2C receptor. Its properties allow it to be active in the central nervous system, especially in the treatment of major depression, seasonal affective disorder, sleep disorder, cardiovascular diseases, diseases of the digestive system, insomnia and fatigue caused by jet lag, appetite disturbance and obesity. Agomelatine is the first melatoninergic antidepressant, and is effective for the treatment of depression, the improvement of sleep parameters and the maintenance of sexual function. The preparation and therapeutic use of agomelatine have been reported in the European patent EP0447285.
In view of the pharmaceutical value of agomelatine, it is critical to obtain the said compound in a highly pure, and stable crystalline form as well as with good reproducibility so that it will be advantageous in pharmaceutical formulations and stable enough for long-term storage without specific requirements regarding temperature, light, humidity or oxygen levels.
Chinese Patents CN200510071611.6, CN200610108396.7, CN200610108394.8 and CN200610108395.2 have respectively disclosed the crystalline forms II, III, IV, V of agomelatine and the preparations thereof.
Among these, crystalline form II is prepared by recrystallization from ethanol and water; crystalline form III is prepared by heating agomelatine at 110° C. until complete melting occurs and then slowly cooling down until formation of the crystal; crystalline form IV is prepared by heating agomelatine at 110° C. until complete melting occurs, followed by rapidly cooling down to 50-70° C. and maintaining at 70° C. for about 5 h until formation of the crystal occurs; crystalline form V is prepared by so-called “high-energy” mechanical grinding of agomelatine.